Method of visualizing an electrostatic charge image by exposure to charged particlesof boron oxide



Feb. 7, 1967 c. B. J. D'ARTAGNAN ALBRECHT ETAL 3,303,027

METHOD OF VISUALIZING AN ELECTROSTATIC CHARGE IMAGE BY EXPOSURE TOCHARGED PARTICLES 0F BORON OXIDE Filed June 4, 1964 I INVENTOR.CORNELIUS B.J.D ARTAGNAN ALBRECHT United States Patent 3,303,027 METHODOF VISUALIZING AN ELECTROSTATIC CHARGE IMAGE BY EXPOSURE TO CHARGEDPARTICLES OF BORON OXIDE Cornelius Berthold Josef DArtagnan Albrecht andPetrus Cornelis van der Linden, Emmasingel, Eindhoven, Netherlands,assignors to North American Philips Company, Inc., New York, N .Y., acorporation of Delaware Filed June 4, 1964, Ser. No. 372,517 Claimspriority, application Netherlands, June 6, 1963, 293,748 5 Claims. (Cl.96-1) The invention relates to a method of visualizing an electrostaticcharge image on an image carrier by means of finely divided material,which carrier is suitable for repeated use.

Such methods, with variations, by which a visible image is obtainedthrough an electrostatic latent charge image, are known. As finelydivided material by means of which the latent image is visualized, useis made of all kinds of pulverulent substances, preferably resinoussubstances, such as rubber copal, rubber sandarac, coumarone indeneresin, resin-resin or other substances such as lycopodium, talcum; sootor aluminum bronze. After a charge image has been visualized and beforea new charge image has been applied to the charge carrier, the powderor, in case the image is transferred to another carrier to obtain apermanent print, the remainder of the powder should be thoroughlyremoved. To this end also several methods are known. The powder may beremoved by brushing, in which event an electrostatic field mayfacilitate this rushing operation, in certain cases, the powder may beblown away by compressed air. It has also been suggested for thispurpose to cause granular material having a polarity opposite to that ofthe powder to flow over the image carrier.

These known methods of cleaning the image carrier all have one or moredisadvantages. Either it is diflicult to remove the whole remainder ofpowder, or the image carrier is readily damaged, or the method iscircuitous. In the long run, damage of the image carrier adverselyaffects the quality of the image.

The method in accordance with the invention provides the possibility ofremoving the powder image without touching the image carrier. Moreover,the measures required for removing the powder image are simpler withthis method than with the known methods.

The invention is characterized in that the charge image is visualized bymeans of finely divided boron oxide.

At low temperature, boron oxide has a comparatively high vapor tension.If, for example, the image carrier is left for l to 2 hours at roomtemperature, the boron oxide has disappeared as a result of sublimation.Preferably, it is heated to a temperature of at least approximately 40C.; the rate of sublimation is then sufiiciently high to remove thepowder from the image carrier within a reasonable time, that is to sayof the order of 1 minute.

It should be noted that xerographic plates exhibit fatigue phenomenaafter they have been charged and discharged several times. It is knownto regenerate the xerographic plate by heating the latter to atemperature of approximately 40 C to 60 C. Consequently, when use ismade of a xerographic image carrier, use of the invention has theadvantage that the regeneration of the plate and the removal of theremainder of boron oxide are carried out in one operation.

In the most suitable method of visualizing an electrostatic latentcharge image in accordance with the invention, an organic boron compoundis burned, while the fumes thereof are brought in the proximity of thecharge I print.

image. For example, this compound is the boric acid triethyl ester.

A further preferred embodiment of the method in accordance with theinvention consists in that the fumes originating from the organic boroncompound are guided through an electric discharge. Consequently, theboron oxide particles are statically charged, as a result of which theselectivity with which the boron oxide particles are deposited on thecharge image is improved and the rate of deposition is increased. Thismethod also provides the possibility of converting the latent chargeimage at will into a negative visible image or into a positive visibleimage by choice of the polarity of the potential of the image carrierand of the boron oxide particles respectively.

In the method in accordance with the invention use is preferably made ofan electrostatic latent charge image obtained by exposure to lightaccording to an image pattern on a carrierat least the surface of whichconsists of photoconductive material. Such materials are known for thispurpose. Examples are: solenium, anthracene, anthraquinone, sulphur,mixtures of anthracene and sulphur and mixtures of selenium and sulphur.

The thermal treatment for removing the boron oxide may be carried out inknown manner. For this purpose, heating by means of infrared radiationis very suitable. Moreover, a further usual possibility of improvingthat is to say of intensifying, the image contrast is obtained. For thispurpose, the surface of the image carrier should have a high coeflicientof absorption for this radiation. At the areas at which the quantity ofboron oxide present per surface unit is small, the boron oxidesublimates more rapidly than at areas at which the quantity present persurface unit is larger. During the radiation, the contrast variation ofthe image can be followed and the radiation can be stopped when thedesired quality is obtained.

The boron oxide is white-colored and an image obtained by the method inaccordance with the invention can be observed on a contrastingsubstratum with normal light. When the substratum has a low contrastingaction or a strong reflection, the image can be observed with laterallyincident light.

An electrostatic image in itself is distinguished by a satisfactoryeffect, while it also has an excellent definition.

An'image consisting of boron oxide is not particularly suitable fortransfer to a carrier to obtain a permanent In practice, however, thereare several cases in which the image obtained is only observed orphotographed.

An image-projection system is known, for example, for the projection ofradar images from a cathode-ray tube, in which use is made of an endlessbelt on which a plurality of plates having a photoconducting surface areprovided. Each plate is provided with a uniform electrostatic charge andexposed in that the image of the screen of the cathode-ray tube isprojected thereon, whereupon the charge image thus obtained isvisualized by means of powder and this image is epidiascopicallyprojected onto a screen; finally, the powder is removed from the' plate.Use is made of several, for example three, projectors each of whichprojects the image of one of a plurality of successive platessuperimposed one on the other onto one screen. In this image-projectionsystem, the method in accordance with the invention may advantageouslybe used.

Another possibility of using the invention resides in the fact that on aphoto-conducting plate provided with an electrostatic charge, an X-rayimage can be directly con verted into a charge image, consequentlywithout the in termediary of a luminescent screen. In this manner, animage is obtained which has a much greater definition than can berealized with photographic paper sensitive to X-rays or with theintermediary of a luminescent screen. The definition thus obtained is200 lines/mm., as can be proved with the aid of photographs of very finegauze, whereas the definition of X-ray films is only 100 lines/cm.

Excellent photographs can be made of the powder image, so that on thefilm details are obtained in the X-ray image which cannot be realizedwith other methods of fixing the X-ray image on the film.

The invention will now be described more fully with reference to theaccompanying drawing.

FIG. 1 is a cross-sectional view of a casing in which an electrographicimage carrier 1 is disposed. The image carrier 1 consists of a polishedselenium plate having dimensions of 13 x 18 cms. The casing itselfconsists of an aluminum frame in one side 2 of which provision is madeof a slot provided with a light-tight closure, through which slot theimage carrier can be introduced. The image carrier is electricallyinsulated from the casing by means of material 3. A suitable cover 4covers the image side of the selenium plate in a light-tight manner andcan be slid 'away when the charge is provided, the exposure is carriedout and the image-producing powder is removed.

The selenium plate is charged in the open casing in the absence of lightwith the aid of a punctiform electrode which is brought to a potentialof +25 kv. with respect to earth. This charging process lasts 1 minute:the charge on the plate then is 4 A./ sec. (4 coul.).

An X-ray shadow image is directly projected onto the plate thus charged,which results in a negative consisting of positive charges. In theinterval between the charging and the irradiation of the selenium plate,the casing is closed of course. As shown in FIG. 2, the closed casing isnow disposed on a chamber 5 which is open on the upper side, this openside being completely covered by the casing. The slide 4 is opened. Onthe lower side of the chamber provision is made of a funnel-shaped inlet6 which projects together with a tube 7 into the chamber through thebottom thereof. Below the funnel 6, a spirit burner 9 is disposed whichis filled with triethyl borate. In the tubular inlet 7, an electrode 8is disposed which is brought to a potential of --10 kv., with respect toearth. The spirit burner is lighted and the fumes of boron oxide hydraterise through the funnel, are charged negatively and reach the positivelycharged image on the selenium plate. The powder image has formed afterto seconds. If this powder image is photographed with laterally incidentlight, the positive X-ray image is directly obtained on the photographicplate.

The powder image is removed in that the selenium plate is heated to atemperature of approximately C. for 2 to 4 minutes. This thermaltreatment may be carried out, for example, by subjecting the rear sideof the selenium plate to a hot air current.

What is claimed is:

1. In a method of xerographic reproduction including the steps ofproviding an electrostatic charge on a photoconducting carrier,irradiating the charged carrier to produce an electrostatic latent imagethereon, forming a visual image on said carrier corresponding to saidelectrostatic latent image, and heating said carrier to remove thevisual image and regenerate the carrier, the improvement comprising thestep of exposing the electrostatically charged carrier to chargedparticles of boron oxide to form a visual photographic image.

2. A method as claimed in claim 1 in which boron oxide is removed fromthe image carrier by heating the latter to a temperature ofapproximately 40 C. to C.

3. A method as claimed in claim 1 in which boron oxide is obtained byburning an organic boron compound.

4. A method as claimed in claim 1 in which at least the surface of theimage carrier more strongly absorbs heat radiation than boron oxide andthat after the boron oxide is provided, the side of the carrier coatedtherewith is subjected to heat radiation to obtain an increase ingradation.

5. A method of fixing an X-ray image as claimed in claim 1 in which thecarrier is exposed to 'X-ray radiation to form an electrostatic chargeimage and the visual image is photographed with laterally incidentlight.

References Cited by the Examiner UNITED STATES PATENTS 2,691,345 10/1954 Huebner 25262.l 2,863,767 12/1958 Vyverberg et al. ll7l7.53,178,281 4/1965 Jarvis 250-- RALPH G; NILSON, Primary Examiner.

W. F. LINDQUIST, Assistant Examiner.

1. IN A METHOD OF XEROGRAPHIC REPRODUCTION INCLUDING THE STEPS OFPROVIDING AN ELECTROSTATIC CHARGE ON A PHOTOCONDUCTING CARRIER,IRRADIATING THE CAHRGED CARRIER TO PRODUCE AN ELECTROSTATIC LATENT IMAGETHEREON, FORMING A VISUAL IMAGE ON SAID CARRIER CORRESPONDING TO SAIDELECTROSTATIC LATENT IMAGE, AND HEATING SAID TO REMOVE THE VISUAL IMAGEAND REGENERATE THE CARRIER, THE IMPROVEMENT COMPRISING THE STEP OFEXPOSING THE ELECTROSTATICALLY CHARGED CARRIER TO CHARGED PARTICLES OFBORON OXIDE TO FORM A VISUAL PHOTOGRAPHIC IMAGE.